OK, I got the standard FSB off my Bushy HBAR 11.5". I'm gonna have AR15barrels.com proifile to a much lighter shape. Then I'd like to put a low profile gas block on and do a full float forestock. Anyway, since the FSB and barrel are drilled together (at the factory by Bushmaster), how will I get the new low profile gas block to fit the old holes? Sorry for the noob question, any help welcome.